This invention relates to cartridge cases, and more particularly to composite cartridge cases made up of a plurality of component parts, including a tubular casing body having a mouth portion for receiving a projectile, and a separate head assembly for reinforcing the base of the cartridge case and mounting a primer component. The principal purpose of such a composite construction is to permit the use of dissimilar materials for the components, usually comprising plastic for the casing body and metal for the head assembly, thereby conserving the relatively scarce and expensive metal. Examples of such composite cases are described and claimed, for example, by U.S. Pat. No. 3,745,924 issued July 17, 1973 to John J. Scanlon, and by U.S. patent application Ser. NO. 320,328, filed on Jan. 2, 1973 by H. Jackson Hale, and now Pat. NO. 3,874,294 both of which are assigned to the owner of this application. The mouth portion of the case may be integrally formed in the casing body, or may be a separate insert, usually of metal. A composite case of the latter type is described and claimed by U.S. Pat. No. 3,842,739 issued Oct. 22, 1974 to John J. Scanlon et al., and also assigned to the owner of this application.
The general objects of the present invention are to provide an improved method for manufacturing composite cartridge casings, and a casing which exhibits a high degree of structural integrity against the development of cracks or other mechanical failures under the high pressures and temperatures developed by firing the cartridge. Other objects and advantages of the invention will appear as the following description proceeds.
Briefly stated, according to a preferred mode of practice of the improved method, a tubular casing body is formed, preferably from a suitable synthetic resin or plastic material according to well-known procedures, with an open-ended breech portion having an interior cylindrical wall extending to an opening at a base end of the casing. A rearwardly-facing shoulder is formed about the interior wall in spaced-apart relation to the base. The casing body is also formed with a mouth portion at a forward end, dimensioned to receive a selected bullet or projectile in mechanically-secured gas-sealing relation; the mouth portion may be molded integrally in the casing body, or may comprise a separate tubular metallic insert.
A bridge insert member is formed, also preferably from a suitable synthetic resin or plastic material, with a forward cup portion having a cylindrical outer wall which is of a diameter to be slidable into the interior of the casing through the base opening, and with a rearward annular skirt portion of a reduced diameter. It preferably also has a central frusto-conical portion connecting the cup and skirt portions, a primer-receiving recess in the skirt portion, and a transverse wall portion formed centrally with a flash hole to communicate the primer recess with the powder charge to be contained in the body of the casing.
The bridge insert is inserted through the base opening into abutment with the shoulder on the interior wall, which is preferably spaced somewhat farther from the base of the casing than the length of the bridge insert, to provide a suitable length of overhanging material in the breech portion of the casing for the ensuing step. This consists of deforming, preferably by cold-working, a rearward region of the breech portion of the casing to reduce its diameter and bring it into conforming circumferential engagement with the exterior surfaces of the frusto-conical and skirt portions of the bridge insert, thereby securing the assembly of the casing body and bridge insert. The outer surface of the breech portion thus assumes a form similar to that of the bridge insert, and provides an extraction groove at the base of the casing. A head assembly, preferably formed of metal and including a reinforcing sleeve, an extraction rim, and a cup member, is then attached to the base of the casing according to methods known per se.